This invention relates to a method for the continuous addition of glue to a mixture consisting of wood chips, wood fibres or the like and to a mixer for carrying out this method.
A method and a mixer of the type above-mentioned are known from the U.S. Pat. No. 3,734,471 in which small centrifugal glue tubes are mounted on a shaft which tubes end in the ring of mixture and to which the glue is supplied without pressure through the shaft which is of hollow construction. In this case, the distribution of the glue over the chips is effected predominantly by a so-called wiping effect, that is to say the chips travelling past the openings of the centrifugal glue tubes wipe off glue which is further distributed over the surfaces of the chips in an after-mixing zone and is also transferred to other chips. These mixers have proved extremely successful in practice but suffer from the disadvantage that the distribution of the glue was effected with a very high introduction of energy which led, on the one hand to a partial destruction of the coarse chips which are important for the strength of chipboards, and on the other hand to a considerable use of energy.
From German Auslegeschrift No. 2134305, it is known to supply the glue, largely without pressure, through small glue tubes which are taken into the mixing container from the outside and end in the ring of mixture. As a result of this construction, cleaning of the glue supply tubes is facilitated, in particular, with substantially the same effect.
From German Gebrauchsmuster No. 7112402, it is known, in a ring mixer, to deliver the glue through small centrifugal glue tubes, projecting radially from the shaft, into the space situated inside the ring of mixture. A satisfactory distribution of the glue over the chips is not possible by this means; instead the risk of glue and spots of glue breaking through is very great. For this reason, in this known mixer, it was additionally provided to provide also small glue feed tubes projecting into the mixing container from the outside and ending with their outlets in the ring of mixture, in order to achieve a more or less satisfactory distribution of glue over the individual chip fractions. Apart from this, the problems of high introduction of energy and destruction of chips caused thereby also occur in this mixer.
From U.S. Pat. No. 4,390,285, it is known to introduce the glue into the ring of mixture from the outside through glue-air nozzles disposed substantially flush with the container wall.
Finally, from U.S. Pat. No. 3,163,403, it is known to introduce plasticizers into plastics materials for the production of a so-called dry blend, in such a manner that the plasticizer is supplied through the shaft of a mixer and is introduced, through nozzles, into the interior space inside a ring of mixture consisting of plastics particles. The working of the plasticizer into the plastics and not on its surface is effected by the required high introduction of energy by means of the mixing mechanism. In this case problems of destruction of the particles by the excessive introduction of energy do not arise.